class Compiler {
    constructor (vm) {
        this.el = vm.$el
        this.vm = vm
        this.compile(this.el)
    }
    // 编译模板，处理文本节点和元素节点
    compile (el) {
        let childNodes = el.childNodes     // 子节点
        Array.from(childNodes).forEach(node => {
            // 处理文本节点
            if (this.isTextNode(node)) {
                this.compileText(node)
            } else if (this.isElementNode(node)) {
                // 处理元素节点
                this.compileElement(node)
            }

            // 判断node节点，是否有子节点，如果有子节点，要递归调用compile
            if (node.childNodes && node.childNodes.length) {
                this.compile(node)
            }
        })
    }
    // 编译元素节点，处理指令
    compileElement (node) {
        // console.dir(node.attributes)
        // 遍历所有的属性节点
        Array.from(node.attributes).forEach(attr => {
            // 判断属性节点是否是指令
            let attrName = attr.name
            if (this.isDirective(attrName)) {
                // v-text --> text
                attrName = attrName.substr(2)
                let key = attr.value
                this.update (node, key, attrName)

                // 判断是否是处理事件的指令
                if (this.isEventDirective(attrName)) {
                    this.eventHandler(node, this.vm, attrName, key)
                }
            }
        })
    }
    // 判断是否是处理事件的指令
    isEventDirective (attrName) {
        return attrName.indexOf('on') === 0
    }

    eventHandler (node, vm, attrName, fnName) {
        let eventType = attrName.substr(attrName.indexOf(':') + 1)
        let fn = this.vm.$options.methods && this.vm.$options.methods[fnName]
        fn && node.addEventListener(eventType, fn.bind(this.vm))
    }    

    update (node, key, attrName) {
        let updateFn = this[attrName + 'Updater']
        updateFn && updateFn.call(this, node, this.vm[key], key)
    }

    // 处理v-text指令
    textUpdater (node, value, key) {
        node.textContent = value
        new Watcher(this.vm, key, (newValue) => {
            node.textContent = newValue
        })
    }
    // v-model
    modelUpdater (node, value, key) {
        node.value = value
        new Watcher(this.vm, key, (newValue) => {
            node.value = newValue
        })
        // 双向绑定
        node.addEventListener('input', () => {
            this.vm[key] = node.value
        })
    }
    // v-html
    htmlUpdater (node, value, key) {
        node.innerHTML = value
        new Watcher(this.vm, key, (newValue) => {
            node.innerHTML = newValue
        })
    }
    // v-on
    // onUpdater (node, value, key) {
    //     let reg = /^@|^v-on:/
    //     let value = node.textContent
    //     if (reg.test(value)) {
    //         let key = RegExp.$1.trim()
    //         node.textContent = value.replace(reg, this.vm[key])
        
    //         // 创建watcher对象，当数据改变更新视图
    //         new Watcher(this.vm, key, (newValue) => {
    //             node.textContent = newValue
    //         })
    //     }
    }

    // 编译文本节点，处理插值表达式
    compileText (node) {
        let reg = /\{\{(.+?)\}\}/
        let value = node.textContent
        if (reg.test(value)) {
            let key = RegExp.$1.trim()
            node.textContent = value.replace(reg, this.vm[key])
        
            // 创建watcher对象，当数据改变更新视图
            new Watcher(this.vm, key, (newValue) => {
                node.textContent = newValue
            })
        }
    }
    // 判断元素属性的名字，是否是指令
    isDirective (attrName) {
        return attrName.startsWith('v-')
    }
    // 判断传入节点是否是文本节点
    isTextNode (node) {
        return node.nodeType === 3
    }
    // 判断节点是否是元素节点
    isElementNode (node) {
        return node.nodeType === 1
    }
}